RE: Please see this thread at Microsoft Community: http://answers.microsoft.com/en-us/windows/forum/windows_8-gaming/windows-8-xbox-live-games-gamertag-change/2d6ae0e3-44be-41b3-80c1-1328bf6f06ca
You cannot play Microsoft Solitaire or Minesweeper, you need a XBOX Gamertag. It will be automatically generated for you, Windows user cannot select it by him/herself. To change the gamertag is possibly only from XBOX, which I do not own nor will I get one, or from inside a game running on Games on Windows LIVE platform which Microsoft recently shut down.
My question: is it really true that a Windows 8 user needs to buy an extra XBOX just to be able to fully utilize the XBOX Live account?